These data are macroinvertebrate composition and abundance in eight Welsh upland rivers with contrasting land-use, moorland and exotic conifer, in response to riparian deciduous leaf addition. Eight sampling reaches were chosen at two sites, Llyn Brianne (4 reaches) and Plynlimon (4 reaches). The experiment consisted of adding deciduous leaves to half of the reaches whilst the other half were maintained as control (no addition). Nylon mesh bags containing deciduous leaves were fixed in both experimental and control reaches to estimate leaf decomposition rates. The macroinvertebrate composition of the nylon mesh bags was surveyed in January 2013 and again in March 2013 in each sampling reach. The main goal of this survey was to examine how aquatic biodiversity responds to leaf addition in moorland and conifer forested rivers. Dr Isabelle Durance was responsible for organising the surveys, Dr Hugh Feeley, Dr Dan Perkins and Marian Pye were in charge of collecting, processing and sorting the invertebrate samples. The work was carried out under Diversity in Upland Rivers for Ecosystem Service Sustainability (DURESS) project (Grant reference NERC NE/J014818/1). DURESS was a project funded by the Natural Environment Research Council (NERC) Biodiversity and Ecosystem Service Sustainability (BESS) programme Full details about this dataset can be found at https://doi.org/10.5285/3e6a9ffd-59f2-48ea-840b-1582dc6c1e3d
